1. Field of the Invention
This invention relates to a process for preparing 3-phenacylidene phthalides useful as growth regulants for plants and safering agents to reduce herbicidal injury to plants.
2. Description of the Prior Art
3-Phenacylidene phthalides are known to have various effects on plants. For instance, according to B. T. Brown and G. F. Katekar et al, it has been reported that the phthalides act to inhibit root geotropism of cress and rygrass seedlings [Experientia, 28, 1290 (1972); Pesticide Science, 4, 473 (1973); Phytochemistry, 15, 1421 (1976); Plant Physiology, 68, 1460 (1981)]. J. A. Hubion et al reported that the phthalides have utility as a growth regulants [U.S. Pat. No. 4,255,181 (1981)] and utility as safering agents to reduce herbicidal injury to plants [U.S. Pat. No. 4,182,622 (1980)].
For the preparation of 3-phenacylidene phthalides, there are known processes using the following reaction sequences (1) and (2) (described in the above literature) and (3) a process set forth in Journal of Chemical Society, Perkins Transaction I, 635 (1975). ##STR2## in which Rs are substituents capable of substitution at any position of the benzene nucleus and may be different or the same, and represent a hydrogen atom, a halogen atom or a linear or branched alkyl, alkenyl or alkoxy group having from 1 to 18 carbon atoms, and n is an integer of from 1 to 5.
However, all these processes require expensive staring materials and also skills in proceeding reaction and are not adapted for the preparation of the phthalides in large amounts.